Hearing loss has occurred in 45 percent of 280 renal patients studied, and the cause is obscure in 20 percent of those affected. In another group risk factors are present, but hearing loss has not occurred. Detailed scrutiny and statistical analysis are being applied to these groups to determine what heretofore unknown factors might contribute to the hearing loss in one instance or protect against loss in the other. Non-ototoxic medications, results of clinical laboratory tests, blood pressures, types of dialysis coil and type of renal transplant are representative of the data being examined. Serial audiograms, including special tests, are being done to determine incidence, probable site of lesion and whether or not losses remain stable or worsen, allowing for aging. Vestibular analysis of 32 patients showed abnormalities in 53 percent; 60 percent of them appeared to involve the end-organ. More electronystagmographic data is being accumulated. Longitudinal clinical, audiological and vestibular studies are in progress for the five years of the project. Nearly 400 patients are under study. Temporal bones were examined in 25 patients who died. Pathology varied widely. In two cases whose cause was obscure clinically the findings suggested vascular etiology. Temporal bone studies continue.